What type of a buoy has a white with blue band?

A buoy that is white with a blue band typically indicates a special purpose or special use. In many regions, this type of buoy is often used to mark areas such as Scuba diving zones, fish aggregating devices, or other specific marine activities. The color scheme is designed to stand out and convey important information to mariners. Always refer to local nautical charts for specific meanings as they can vary by region.